B-tube reform for improved thermal cycle performance

ABSTRACT

A tube for use in a heat exchanger includes an upper portion, a base portion spaced from the upper portion, and a partitioning wall depending from the upper portion. The partitioning wall is bent away and spaced from the base portion in a first section of the tube to form a single flow channel within the tube along the first section. The partitioning wall contacts the base portion in a second section of the tube to form a partition separating a first flow channel from a second flow channel along the second section. The first section of the tube is configured for reception into an opening of a header tank of the heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a divisional patent application of U.S.patent application Ser. No. 15/697,754 filed Sep. 7, 2017, which claimspriority to U.S. Provisional Patent Application Ser. No. 62/408,570,filed Oct. 14, 2016, the entire disclosure of which is herebyincorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a heat exchanger, and more specifically, to aheat exchanger including a B-shaped flat tube having a reformed tube endfor attachment to a header tank of the heat exchanger.

BACKGROUND OF THE INVENTION

Heat exchangers having folded flat tubes are well known in the art. Suchheat exchangers typically include a plurality of the folded flat tubesspaced apart and arranged in parallel and extending between an inletheader tank and an outlet header tank. The inlet header tank receives afirst fluid and distributes the first fluid between a plurality of flowpathways formed within the flat tubes. The first fluid exchanges heatenergy with a second fluid flowing through the spaces between adjacentones of the flat tubes. After exchanging the heat energy within the flattubes, the first fluid is recombined within the outlet header tankbefore exiting the heat exchanger.

One common construction of a flat tube includes folding a sheet ofaluminum into a tubular structure wherein two opposing edges of thesheet are brought together and then brazed or welded at the resultingseam to form a substantially B-shaped flat tube. The central seam of theB-shaped flat tube is typically further reinforced by adding at leastone fold to the opposing edges of the sheet. The folded over portions ofthe sheet of aluminum are positioned to abut an inner surface of theflat tube along a length thereof to form a longitudinally extendingpartition, wherein the partition divides a hollow interior of each ofthe flat tubes into two flow separate paths while also structurallyreinforcing the flat tube along the central seam of the tube. This typeof flat tube construction is disclosed in U.S. Pat. No. 5,579,837 to Yuet al., which is hereby incorporated by reference in its entirety.

One potential issue faced by the traditional B-shaped flat tubeconstruction occurs as a result of the effects of thermal cycling. Therepeated presence of varying characteristics within different portionsof each of the tubes, such as varying temperatures experienced indifferent regions of each of the tubes, may lead to the formation of abending moment within each of the tubes, such as between two adjacentflow channels formed within each of the tubes. The formation of suchbending moments may affect the durability of such tubes when exposed toextended periods of thermal cycling. including varying temperaturesexperienced between the two flow channels of each of the tubes.

The B-shaped folded flat tube construction has been found to beparticularly susceptible to thermal cycling failure at an intersectionof each of the tubes and each of the header tanks. Each of the tubes isinserted into an opening formed in each of the header tanks, the openinghaving a cross-sectional shape substantially similar to that of an outersurface of each of the tubes, thereby restricting outward deformation ofthe outer surface of each of the tubes. Concurrently, the centralpartition adds rigidity to the interior of each of the tubes furtherrestricting relative movement between the opposing surfaces of each ofthe tubes adjacent the central partition. The added rigidity adjacentthe intersection of each of the tube ends and each of the header tanksexacerbates the incidence of failure due to thermal cycling because thedifferent portions of the tubes experiencing different degrees ofthermal expansion are restricted from moving and deforming relative toeach other during use of the heat exchanger. The restricted motion mayin some circumstances lead to elevated stresses within portions of eachof the tubes that can lead to permanent deformation or eventual failureadjacent each of the header tanks.

It would therefore be desirable to produce a tube for use in a heatexchanger having multiple flow channels while also preventing theincidence of failure at an intersection of the tube and an opening in aheader tank configured to receive an end of the tube.

SUMMARY OF THE INVENTION

Compatible and attuned with the present invention, a tube having amodified reinforcing structure for preventing the incidence of failureat an intersection of the tube and an opening in a header tankconfigured to receive an end of the tube has surprisingly beendiscovered.

In one embodiment of the invention, a tube for use in a heat exchangercomprises an upper portion, a base portion spaced from the upperportion, and a wall depending from the upper portion. The wall is spacedfrom the base portion in a first section of the tube and the wallcontacts the base portion in a second section of the tube to form apartition.

In another embodiment of the invention, a heat exchanger comprises afirst header tank including a first opening providing fluidcommunication with an interior of the first header tank and a tubeincluding an upper portion, a base portion spaced from the upperportion, and a wall depending from the upper portion. The wall is spacedfrom the base portion in a first section of the tube and the wallcontacts the base portion in a second section of the tube to form apartition. A first portion of the first section of the tube extends intothe interior of the first header tank through the first opening.

In another embodiment of the invention, a method of forming a heatexchanger is disclosed. The method comprises the steps of bendingopposing end regions of a sheet of material toward each other to form atube having an upper portion spaced from a base portion, the opposingend regions of the sheet cooperating to form a partitioning wallextending from the upper portion to the base portion and dividing thetube into a pair of flow channels; bending the partitioning wall awayfrom the base portion along a first section of the tube to form a firstsingle flow channel along the first section; and inserting a firstportion of the first section of the tube into an interior of a firstheader tank through a first opening formed therein.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as other objects and advantages of the invention,will become readily apparent to those skilled in the art from readingthe following detailed description of a preferred embodiment of theinvention when considered in the light of the accompanying drawings:

FIG. 1 is an elevational view of a heat exchanger for a motor vehicleaccording to an embodiment of the invention;

FIG. 2 is a cross-sectional view of a tube for use in the heat exchangerillustrated in FIG. 1 prior to a bending of a partitioning wall thereof;

FIG. 3 is a perspective view of a sheet of material for forming thecross-sectional shape of the tube illustrated in FIG. 2;

FIG. 4 is a fragmentary top plan view of the tube of FIG. 2;

FIG. 5 is a cross-sectional elevational view of an interior of the tubeof FIG. 2 taken through section lines 5-5 of FIG. 4 prior to a bendingof a partitioning wall of the tube;

FIG. 6 is a cross-sectional elevational view of the interior of the tubeof FIG. 2 as taken through section lines 5-5 of FIG. 4 following thebending of the partitioning wall of the tube;

FIG. 7 is a fragmentary cross-sectional view of an interior of the tubeof FIG. 2 following the bending of the partitioning wall of the tube;

FIG. 8 is a fragmentary cross-sectional view of an interior of the tubeof FIG. 2 following the bending of the partitioning wall according toanother embodiment of the invention;

FIG. 9 is a fragmentary cross-sectional view of an interior of the tubeof FIG. 2 following the bending of the partitioning wall according toanother embodiment of the invention; and

FIG. 10 is a fragmentary cross-sectional view of a heat exchanger havingthe tubes illustrated in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description and appended drawings describe andillustrate various embodiments of the invention. The description anddrawings serve to enable one skilled in the art to make and use theinvention, and are not intended to limit the scope of the invention inany manner. In respect of the methods disclosed, the steps presented areexemplary in nature, and thus, the order of the steps is not necessaryor critical.

FIG. 1 illustrates a heat exchanger 10 according to an embodiment of theinvention. The heat exchanger 10 may be used in an automotiveapplication such as forming a portion of a heating, ventilating, and airconditioning (HVAC) system or a portion of a cooling system forregulating a temperature of one or more components of the automobile, asdesired. The heat exchanger 10 may form an evaporator, a condenser, or aradiator of the motor vehicle, as non-limiting examples. The heatexchanger 10 may alternatively be used for any application requiring theexchange of heat energy between two or more fluids, as desired.

The heat exchanger 10 generally comprises a first header tank 12, asecond header tank 16, and a plurality of heat exchanger tubes 20extending longitudinally between the first header tank 12 and the secondheader tank 16. The first header tank 12 includes at least one firstfluid opening 13 for conveying a first fluid to or from the first headertank 12 and the second header tank 16 includes at least one second fluidopening 17 for conveying the first fluid to or from the second headertank 16. The first fluid may be a coolant associated with a coolingsystem of the motor vehicle or a refrigerant associated with the HVACsystem of the motor vehicle. In the embodiment illustrated in FIG. 1,the first fluid is configured to flow in order through the first headertank 12, the plurality of the tubes 20, and the second header tank 16,wherein the first fluid opening 13 forms an inlet port of the firstheader tank 12 and the second fluid opening 17 forms an outlet port ofthe second header tank 16. However, it is understood that the heatexchanger 10 may be passable in a reverse flow direction, wherein thefirst fluid flows in order through the second heat exchanger 16, theplurality of the tubes 20, and the first heat exchanger 12 withoutaltering the scope of the present invention.

A plurality of serpentine or convoluted fins 18 may be disposed inspaces formed between adjacent ones of the tubes 20. The spaces formedbetween the adjacent ones of the tubes 20 are configured to receive asecond fluid such as air, for exchanging heat energy between the secondfluid and the first fluid conveyed within the plurality of the tubes 20.The fins 18 are configured to increase a surface area of the heatexchanger 10 exposed to the flow of the second fluid to increase anefficiency of heat transfer between the first and second fluids.

Each of the tubes 20 has a cross-sectional shape including a baseportion 22, a first side portion 24 extending from a first end of thebase portion 22, a second side portion 26 arranged opposite the firstside portion 24 and extending from a second end of the base portion 22,a first upper portion 28 extending inwardly from the first side portion24, a second upper portion 30 extending inwardly from the second sideportion 26, a first partitioning portion 32 depending from the firstupper portion 28 towards the base portion 22, and a second partitioningportion 36 depending from the second upper portion 30 towards the baseportion 22. The base portion 22, the first upper portion 28, and thesecond upper portion 30 extend primarily laterally or in a widthdirection of the tube 20 between the first side portion 24 and theoppositely arranged second side portion 26. The first and second sideportions 24, 26 may be substantially arcuate in shape having a desiredradius of curvature, but other shapes may be used without departing fromthe scope of the present invention.

The first partitioning portion 32 includes a first leg 33, a second leg34, and a bend portion 35 connecting the first leg 33 to the second leg34. The first leg 33 extends at least partially in a height direction ofthe tube 20 perpendicular to the width direction thereof. The first leg33 may be disposed at an angle relative to the height direction of thetube 20 as shown in FIG. 2 or the first leg 33 may be arrangedsubstantially parallel to the height direction of the tube 20, asdesired. The bend portion 35 of the first partitioning portion 32 formsa distal surface configured to engage the base portion 22 of the tube20. The second leg 34 may be arranged at an angle with respect to thefirst leg 33 as shown in FIG. 2 or the second leg 34 may be arrangedsubstantially parallel to the first leg 33 while extending in anopposite direction, as desired. In some embodiments, the second leg 34may be configured to extend parallel to the base portion 22 wherein boththe bend portion 35 and the second leg 34 are in contact with the baseportion 22. Alternative shapes of the first partitioning portion 32 maybe used without departing from the scope of the present invention.

The second partitioning portion 36 includes a first leg 37, a second leg38, and a bend portion 39 connecting the first leg 37 to the second leg38. The first leg 37 extends at least partially in the height directionof the tube 20 arranged perpendicular to the width direction thereof.The first leg 37 may be disposed at an angle relative to the heightdirection of the tube 20 as shown in FIG. 2 or the first leg 37 may bearranged substantially parallel to the height direction of the tube 20,as desired. The bend portion 39 of the second partitioning portion 36forms a distal surface configured to engage the base portion 22 of thetube 20. The second leg 38 may be arranged at an angle with respect tothe first leg 37 as shown in FIG. 2 or the second leg 38 may be arrangedsubstantially parallel to the first leg 37 while extending in anopposite direction, as desired. In some embodiments, the second leg 38may be configured to extend parallel to the base portion 22, whereinboth the bend portion 39 and a length of the second leg 38 are incontact with the base portion 22. Alternative shapes of the secondpartitioning portion 36 may be used without departing from the scope ofthe present invention.

The first partitioning portion 32 and the second partitioning portion 36cooperate to form a partitioning wall 40 dividing a hollow interior ofthe tube 20 into a first flow channel 42 formed to a first side of thepartitioning wall 40 and a second flow channel 44 formed to a secondside of the partitioning wall 40. The first flow channel 42 and thesecond flow channel 44 may be shaped and dimensioned to be symmetricabout a plane generally defined by the partitioning wall 40, as desired.

The tube 20 is formed by first bending a sheet of a material such asaluminium into the tubular cross-sectional shape illustrated in FIG. 2for delimiting a flow of the first fluid therethrough. For example, withreference to FIG. 3, a sheet 50 of material is marked withlongitudinally extending lines A, B, C, D, E, F, G, and H indicatingdivisions of the sheet 50 corresponding to the features identified inFIG. 2. The first leg 33 of the first partitioning portion 32 is formedin the sheet 50 intermediate the line A and a first side edge 51 of thesheet 50, the second leg 34 of the first partitioning portion 32 isformed intermediate the lines A and B, the first upper portion 28 isformed intermediate the lines B and C, the first side portion 24 isformed intermediate the lines C and D, the base portion 22 is formedintermediate the lines D and E, the second side portion 26 is formedintermediate the lines E and F, the second upper portion 30 is formedintermediate the lines F and G, the first leg 37 of the secondpartitioning portion 36 is formed intermediate the lines G and H, andthe second leg 38 of the second partitioning portion 36 is formedintermediate the line H and a second side edge 52 of the sheet 50.

The bending of the tube 20 into the cross-sectional shape shown in FIG.2 may occur according to the following steps. The sheet 50 may be foldedabout the line A to cause the second leg 34 of the first partitioningportion 32 to be disposed at an angle relative to the first leg 33thereof while also folding the sheet 50 about the line H to cause thesecond leg 38 of the second partitioning portion 36 to be disposed at anangle relative to the first leg 37 thereof. Next, the sheet 50 is foldedabout the lines B and G to complete formation of each of the firstpartitioning portion 32 and the second partitioning portion 36,respectively. The folding of the sheet 50 about the line B causes thefirst partitioning portion 32 to be angled relative to the portion ofthe sheet 50 defining the first upper portion 28 while the folding ofthe sheet 50 about the line G causes the second partitioning portion 36to be angled relative to the portion of the sheet 50 defining the secondupper portion 30.

The sheet 50 is then bent into a substantially arcuate shape betweeneach of the lines C and D and the lines E and F to cause formation ofthe first side portion 24 and the second side portion 26, respectively.The formation of the side portions 24, 26 causes the first partitioningportion 32 to be brought towards the second partitioning portion 36while also causing the first and second upper portions 28, 30 to bearranged substantially parallel to the base portion 22. One skilled inthe art should appreciate that the sheet 50 may be bent in analternative order while still arriving at the same cross-sectional shapeillustrated in FIG. 2, including folding the first legs 33, 37 relativeto the second legs 34, 38 following the bending of the remainder of thetube 20, as one non-limiting example.

Following the initial bending of the tube 20 described hereinabove, thefirst leg 33 of the first partitioning portion 32 abuts the first leg 37of the second partitioning portion 36 to form a seam 54 extending alonga length of the tube 20 in a direction perpendicular to each of theheight direction and the width direction thereof. Additionally, the bendportion 35 of the first partitioning portion 32 is in contact with thebase portion 22 of the tube 20 at a position spaced apart in the widthdirection of the tube 20 from a position the bend portion 39 of thesecond partitioning portion 36 contacts the base portion 22 of the tube20 to form a fillet 56 therebetween. A size of the fillet 56 is based onthe angle formed between the first legs 33, 37 of the first and secondpartitioning portions 32, 36 as well as a height of the tube 20 formedbetween the base portion 22 and the first and second upper portions 28,30.

The tube 20 is generally described as including the base portion 22arranged parallel to the first and second upper portions 28, 30intermediate the first and second side portions 24, 26, but it should beunderstood that those portions of the tube 20 formed to either lateralside of the partitioning wall 40 may have alternative shapes withoutaffecting a use of the tube 20. The tube 20 may for example have flaredlateral regions as is disclosed in pending U.S. Patent ApplicationPublication No. 2014/0196877 to Wilkins et al., which is herebyincorporated herein by reference in its entirety.

The initial process of bending the tube 20 may therefore be summarizedas including the bending of a first end region 71 of the sheet 50, whichextends between the first side edge 51 and the line B and corresponds tothe first partitioning portion 32 of the tube 20, towards a second endregion 72 of the sheet 50, which extends between the second side edge 52and the line G and corresponds to the second partitioning portion 36 ofthe tube 20, to form a closed tubular structure for delimiting a flow ofthe first fluid therethrough. The first end region 71 is additionallybrought into abutment with the second end region 72 in a manner whereineach of the end regions 71, 72 spans the height dimension of the tube 20extending between the base portion 22 and the first and second upperportions 28, 30, thereby forming the partitioning wall 40 for delimitingthe flow of the first fluid into each of the first flow channel 42formed to the first side of the partitioning wall 40 and the second flowchannel 44 formed to the second side of the partitioning wall 40.

After formation of the tube 20 into the shape shown in FIG. 2, asecondary bending process is carried out with respect to thepartitioning wall 40 of the tube 20, as best shown in FIG. 5-7. FIG. 5illustrates a side elevational view of an interior of a first end 21 ofthe tube 20 (with reference to section lines 5-5 as shown in FIG. 4)following the formation of the sheet 50 into the tubular structureillustrated in FIG. 2. A fold line 75 represented by a dashed lineextends along the various surfaces forming the partitioning wall 40 andcorresponds to a line across which a portion of the partitioning wall 40formed adjacent the first end 21 of the tube 20 is folded or bent in acommon direction to one side of the initial position of the partitioningwall 40. The portion of the partitioning wall 40 bent or folded awayfrom the base portion 22 of the tube 20 is hereinafter referred to asthe folded portion 60 of the partitioning wall 40.

The fold line 75 may begin at the first end 21 of the tube 20 adjacentthe seam 54 and extend longitudinally a distance X towards the secondend of the tube 20 until the fold line 75 intersects a lowermostextension of the partitioning wall 40 formed by the bend portions 35, 39of the first and second partitioning portions 32, 36, thereby indicatinga longitudinal end of the folded portion 60 of the partitioning wall 40.The fold line 75 is shown as including at least one inclined portion 76.The inclined portion 76 of the fold line 75 is inclined with respect toa plane generally defined by the base portion 22 of the tube 20. Theinclined portion 76 of the fold line 75 may be rectilinear orcurvilinear and may have a concave or convex shape, as desired. It isunderstood that different forms and configurations of the fold line 75may be used without departing from the scope of the present invention,so long as the partitioning wall 40 is separated from the base portion22 of the tube 20 along a desired length of the tube 20, as explained ingreater detail hereinafter.

In the embodiment illustrated in FIGS. 6 and 7, the partitioning wall 40is folded or bent away from the base portion 22 of the tube 20 in adirection towards each of the first side portion 24 and the first upperportion 28 until the partitioning wall 40 is arranged to extend at leastpartially in the width direction of the tube 20 while spaced apart fromthe base portion 22 of the tube 20. The bending or folding of thepartitioning wall 40 may include deforming the partitioning wall 40about an axis formed adjacent the seam 54 by pivoting a remainder of thepartitioning wall 40 about the axis until a distal end of thepartitioning wall 40 no longer contacts the base portion 22 of the tube20. The process of bending or folding the partitioning wall 40 mayinclude the use of any tool suitable for grasping a desired length ofthe partitioning wall 40 and then translating or pivoting the graspedportion of the partitioning wall 40 to space the partitioning wall 40from the base portion 22 of the tube 20. The bending or folding of thepartitioning wall 40 results in the tube 20 having a single flow channel46 at the first end 21 of the tube 20 along the portions of the tube 20corresponding to the folded portion 60 of the partitioning wall 40.

FIG. 7 illustrates an interior of the tube 20 immediately following thefolding or bending of the folded portion 60 of the partitioning wall 40.The entirety of the partitioning wall 40 depending downwardly from theseam 54 is bent about the axis disposed adjacent the seam 54 until thesecond leg 34 of the first partitioning portion 32 abuts the first upperportion 28 of the tube 20. The first partitioning portion 32 retains thebend portion 35 present between the first and second legs 33, 34 thereofand the second partitioning portion 36 retains the inclusion of the bendportion 39 present between the first and second legs 37, 38. Thus, thefolded portion 60 of the partitioning wall 40 maintains substantiallythe same cross-sectional shape following the folding or bending thereoftoward the first upper portion 28. The folded portion 60 of thepartitioning wall 40 may be further compressed together and towards thefirst upper portion 28 of the tube 20 to cause all of the legs 33, 34,37, 38 of the first and second partitioning portions 32, 36 to bearranged in parallel to reduce a profile of the folded portion 60 of thepartitioning wall 40. The reduction in height of the profile of thefolded portion 60 of the partitioning wall 40 increases a height of thesingle flow channel 46 as it spans the folded portion 60 of thepartitioning wall 40.

The folded portion 60 of the partitioning wall 40 may have alternativecross-sectional configurations without departing from the scope of thepresent invention. For example, FIGS. 8 and 9 show alternativecross-sectional shapes of the folded portion 60 of the partitioning wall40 following a bending or folding of the partitioning wall 40 away fromthe base portion 22 of the tube 20. In FIG. 8, the entirety of the firstand second partitioning portions 32, 36 are bent to extend parallel toeach other as well as each of the base portion 22 and the first upperportion 28 of the tube 20. The bending or folding of the folded portion60 of the partitioning wall 40 therefore includes the removal of thebend portion 35 formed between the first and second legs 33, 34 of thefirst partitioning portion 32 as well as the removal of the bend portion39 formed between the first and second legs 37, 38 of the secondpartitioning portion 36. The removal of the bend portions 35, 39 resultsin the single common flow channel 46 formed at the first end 21 of thetube 20 along the folded portion 60 of the partitioning wall 40 having amaximized spacing between the base portion 22 and the folded portion 60of the partitioning wall 40. FIG. 9 illustrates a cross-sectional shapewherein the second legs 34, 38 of the first and second partitioningportions 32, 36 are folded about an end of the partitioning wall 40 toextend at least partially between the first legs 33, 37 of the first andsecond partitioning portions 32, 36 and the first upper portion 28 ofthe tube 20. It should be understood that the folded portion 60 of thepartitioning wall 40 may be folded to any side thereof and may have anycross-sectional shape so long as the partitioning wall 40 does notcontact the base portion 22 along a selected portion of the tube 20 in amanner dividing the tube 20 into the first and second flow channels 42,44.

Following the folding or bending of folded portion 60 of thepartitioning wall 40, no division exists between the first and secondflow channels 42, 44 along the folded portion 60 and no reinforcingsupport exists between the base portion 22 and the first and secondupper portions 28, 30 of the tube 20. However, the first and secondpartitioning portions 32, 36 of the tube 20 remain in contact adjacentthe first and second upper portions 28, 30 of the tube 20 to allow forthe seam 54 to continue towards the first end 21 of the tube 20, despitethe partitioning wall 40 not contacting the base portion 22 of the tube20 along the folded portion 60 thereof.

The tube 20 may include a second folded portion 60 of the partitioningwall 40 formed at the second end 22 of the tube 20 formed opposite thefirst end 21 thereof. The folded portion 60 of the partitioning wall 40formed at the second end 22 of the tube 20 may be formed in the samemanner as the folded portion 60 of the partitioning wall 40 formed atthe first end 21 thereof. The folded portion 60 of the partitioning wall40 at the second end 22 of the tube 20 may have substantially the samelength and cross-sectional configuration as the folded portion 60 of thepartitioning wall 40 at the first end 21 of the tube 20, as desired. Thefolded portion 60 of the partitioning wall 40 at the second end 22 ofthe tube 20 may for example extend the length X from the second end 22of the tube 20, as desired.

Referring now to FIG. 10, the inclusion of the folded portions 60 of thepartitioning wall 40 at the opposing ends 21, 22 of the tube 20 dividesthe tube 20 into three different sections. A first end section 91includes the folded portion 60 of the partitioning wall 40 at the firstend 21 of the tube 20, a second end section 92 includes the foldedportion 60 of the partitioning wall 40 at the second end 22 of the tube20, and a central section 93 formed intermediate the first and secondend sections 91, 92 includes the partitioning wall 40 contacting thebase portion 22 of the tube 20 to divide the tube 20 into the first andsecond flow channels 42, 44. The first end section 91 and the second endsection 92 may each be formed to have the common length X as measuredfrom each respective end 21, 22 of the tube 20, as desired.

The first end section 91 of the tube 20 is received into a first opening8 formed in an inner wall 4 of the first header tank 12 to position thefirst end 21 of the tube 20 within an interior of the first header tank12. Similarly, the second end section 92 of the tube 20 is received intoa second opening 9 formed in an inner wall 5 of the second header tank16 to position the second end 22 of the tube 20 within an interior ofthe second header tank 16. The openings 8, 9 may have cross-sectionalshapes substantially corresponding to the cross-sectional shape of theexterior of the tube 20 along the first and second end sections 91, 92thereof. The inner wall 4 of the first header tank 12 may be formedintegrally with a remainder of the first header tank 12 or may be aseparate component such as a header plate coupled to the remainder ofthe first header tank 12. Similarly, the inner wall 5 of the secondheader tank 16 may be formed integrally with the remainder of the secondheader tank 16 or may be a separate component such as a header platecoupled to the remained of the second header tank 16.

A first portion of the first end section 91 of the tube 20 extends apreselected distance into the interior of the first header tank 12beyond the first inner wall 4 thereof while a second portion of thefirst end section 91 extends outwardly from the interior of the firstheader tank 12 by a preselected distance Y. The distance Y maypreferably be selected to be in the range of 5-10 mm, but any distancefor the distance Y may be selected without departing from the scope ofthe present invention. The positioning of the tube 20 relative to thefirst header tank 12 results in the first end section 91 of the tube 20spanning the first inner wall 4 to extend at least partially beyond thefirst inner wall 4 in each of two opposing directions. Similarly, afirst portion of the second end section 92 of the tube 20 extends apreselected distance into the interior of the second header tank 16beyond the second inner wall 5 thereof while a second portion of thesecond end section 92 extends outwardly from the interior of the secondheader tank 16 by a preselected distance Z. The distance Z may besubstantially equal to the distance Y or may differ from the distance Y,as desired. The distance Z may preferably be selected to be in the rangeof 5-10 mm, as desired. The positioning of the tube 20 relative to thesecond header tank 16 results in the second end section 92 of the tube20 spanning the second inner wall 5 to extend at least partially beyondthe second inner wall 5 in each of two opposing directions. The centralsection 93 of the tube having the partitioning wall 40 in contact withthe base portion 22 of the tube 20 is disposed intermediate and spacedapart from each of the first header tank 12 and the second header tank16. The central section 93 is shown in fragmentary form in FIG. 10, butit should be understood that the central section 93 may be longer thaneither of the first or second end sections 91, 92 and may have anydesired length, as desired.

At least one surface of each of the sheets 50 used to form the tubes 20is coated with a braze material which is commercially available and wellknown to those skilled in the art. The brazing material may for examplebe placed on a surface of the sheet 50 corresponding to an outermostsurface of the tube 20 following the bending thereof. Once the tube 20has been received into the first and second header tanks 12, 16, theentirety of the heat exchanger 10 may be heated at a predeterminedtemperature to melt the brazing material disposed on the sheet 50forming the tube 20, the brazing flux causing the braze material to flowby capillary flow from the position of the seam 54 and into the brazereceiving fillet area 56. The portion of the seam 54 extending along thefirst and second end sections 91, 92 of the tube 20 is also filled bythe brazing material adjacent the first and second ends 21, 22 of thetube 20 thereof to maintain the integrity of the connection between thetube 20 and each of the header tanks 12, 16 at the seam 54 despite thefolding over of the folded portion 60 of the partitioning wall 40. Thetube 20 is then cooled to solidify the molten braze material in thefillet area 56 to secure the partitioning wall 40 to the base portion 22along the central section 93 of the tube 20. The heating and cooling ofthe braze material concurrently couples each of the tubes 20 to thefirst and second header tanks 12, 16 due to the inclusion of the brazematerial between the outermost surface of the tube 20 and each of theopenings 8, 9 formed in the respective header tanks 12, 16.

It has surprisingly been discovered that the introduction of the foldedportion 60 of the partitioning wall 40 resulting in the absence of areinforcing partitioning wall 40 extending between the first and secondupper portions 28, 30 and the base portion 22 of each of the tubes 20 atthe intersection of the header tanks 12, 16 and each of the tubes 20beneficially results in reduced failure due to thermal cycling of theheat exchanger 10. More specifically, the removal of an intersection ofeach of the base portion 22 of the tube 20, the partitioning wall 40,and a portion of one of the header tanks 12, 16 removes a potential formof failure caused by varying degrees of thermal expansion between eachof the individual components. The positioning of the central portion 93having the partitioning wall 40 contacting the base portion 22 spacedfrom each of the header tanks 12, 16 aids in forming a single flowchannel 46 adjacent the ends 21, 22 of the tube 20 to more uniformlydistribute the thermal energy at the ends 21, 22 of the tube 20 incomparison to a tube having two distinct and separated flow channelsadjacent each of the header tanks. Additionally, the removal of anadditional reinforcing structure adjacent each of the header tanks 12,16 further eliminates a source of stress risers within the ends 21, 22of the tube 20 that could potentially lead to sudden failure of the tube20 during thermal cyclying.

The introduction of the folded portion 60 of the partitioning wall 40aids in preventing failure at the header tanks 12, 16 while alsobeneficially maintaining the seam 54 present between the first andsecond partitioning portions 32, 36 to allow for a manufacturing processsuch as brazing to be applied to the length of the tube 20 to ensurethat separation of the tube 20 does not occur along any of the first endsection 91, the second end section 92, or the central section 93. Thefolded portion 60 also beneficially allows for two or more flow channelsto be formed in the central section 93 of the tube 20 withoutintroducing the potential form of failure at the junction with theheader tanks 12, 16, thereby improving an efficiency of the heatexchanger 10 having the tubes 20.

From the foregoing description, one ordinarily skilled in the art caneasily ascertain the essential characteristics of this invention and,without departing from the spirit and scope thereof, can make variouschanges and modifications to the invention to adapt it to various usagesand conditions.

What is claimed is:
 1. A method of forming a heat exchanger, the methodcomprising the steps of: bending opposing end regions of a sheet ofmaterial toward each other to form a tube having an upper portion spacedfrom a base portion, the opposing end regions of the sheet cooperatingto form a partitioning wall extending from the upper portion to the baseportion to divide the tube into a pair of flow channels; bending thepartitioning wall away from the base portion along a first section ofthe tube to form a first single flow channel along the first section;and inserting a first portion of the first section of the tube through afirst opening formed in a first header tank to provide fluidcommunication between the first single flow channel of the tube and aninterior of the first header tank.
 2. The method according to claim 1,further comprising steps of: coating at least a portion of the tube andat least a portion of the first header tank with a brazing material; andheating the brazing material following the step of inserting the firstportion of the first section of the tube into the interior of the firstheader tank through the first opening.
 3. The method according to claim1, wherein a seam extends along a length of the tube, the seam formed atan intersection of the opposing end regions of the tube.
 4. The methodaccording to claim 1, wherein the partitioning wall is arrangedsubstantially parallel to the upper portion in the first section of thetube.
 5. The method according to claim 1, wherein in a portion of thetube adjacent the first section which includes the pair of flowchannels, the opposing end regions of the sheet of material each contactthe base portion.
 6. The method according to claim 1, wherein theopposing end regions are each spaced from the base portion in the firstsection of the tube.
 7. The method according to claim 1, wherein theopposing end regions overlap in a height direction of the tube in thefirst section of the tube.
 8. The method according to claim 1, whereinin a portion of the tube adjacent the first section which includes thepair of flow channels, the opposing end regions of the sheet of materialeach contact the base portion, wherein the opposing end regions are eachspaced from the base portion in the first section of the tube, andwherein the opposing end regions overlap in a height direction of thetube in the first section of the tube.
 9. The method according to claim1, wherein a second portion of the first section is disposed outside ofthe first header tank.
 10. The method according to claim 9, wherein thesecond portion of the first section has a length in a range of between 5and 10 mm.
 11. The method according to claim 1, further comprising stepsof: bending the partitioning wall away from the base portion along asecond section of the tube to form a second single flow channel alongthe second section; and inserting a first portion of the second sectionthrough a second opening formed in a second header tank to provide fluidcommunication between the second single flow channel of the tube and aninterior of the second header tank.
 12. The method according to claim11, wherein the first section is formed at a first end of the tube andthe second section is formed at a second end of the tube.
 13. The methodaccording to claim 11, wherein a third section of the tube between thefirst section and the second section includes the pair of flow channels,and wherein the opposing end regions of the sheet of material eachcontact the base portion in the third section of the tube.
 14. Themethod according to claim 11, wherein the opposing end regions are eachspaced from the base portion in the first section and the second sectionof the tube.
 15. The method according to claim 11, wherein the opposingend regions overlap in a height direction of the tube in the firstsection and the second section of the tube.
 16. The method according toclaim 11, wherein a third section of the tube between the first sectionand the second section includes the pair of flow channels, and whereinthe opposing end regions of the sheet of material each contact the baseportion in the third section of the tube, wherein the opposing endregions are each spaced from the base portion in the first section andthe second section of the tube, and wherein the opposing end regionsoverlap in a height direction of the tube.
 17. A method of forming aheat exchanger, the method comprising the steps of: bending opposing endregions of a sheet of material toward each other to form a tube havingan upper portion spaced from a base portion, the opposing end regions ofthe sheet cooperating to form a partitioning wall extending from theupper portion to the base portion to divide the tube into a pair of flowchannels; bending the partitioning wall away from the base portion alongan entirety of a first section of the tube to form a first single flowchannel along the first section; inserting a first portion of the firstsection of the tube through a first opening formed in a first headertank to provide fluid communication between the first single flowchannel of the tube and an interior of the first header tank; bendingthe partitioning wall away from the base portion along an entirety of asecond section of the tube to form a second single flow channel alongthe second section; and inserting a first portion of the second sectionthrough a second opening formed in a second header tank to provide fluidcommunication between the second single flow channel of the tube and aninterior of the second header tank; wherein a third section of the tubeis directly connected to the first section and the second section; andwherein the partitioning wall contacts the base portion along anentirety of the third section of the tube.
 18. The method according toclaim 17, wherein the third section of the tube between the firstsection and the second section includes the pair of flow channels, andwherein the opposing end regions of the sheet of material each contactthe base portion in the third section of the tube.
 19. The methodaccording to claim 17, wherein the opposing end regions are each spacedfrom the base portion in the first section and the second section of thetube, and wherein the opposing end regions overlap in a height directionof the tube in the first section and the second section of the tube.